DEF DIGITAL_ROOT N OUT DR,AP
 AP=0
 DR=N
 WHILE DR>9
  INC AP
  STRDR$=STR$(DR)
  NEWDR=0
  FOR I=0 TO LEN(STRDR$)-1
   INC NEWDR,VAL(MID$(STRDR$,I,1))
  NEXT
  DR=NEWDR
 WEND
END